1. Field of the Invention
The present invention relates to a plasma display panel (PDP) and, more particularly, to a structure of electrodes formed on a non-valid screen of the panel and a PDP with the electrodes formed thereon.
2. Description of the Related Art
A plasma display apparatus is an apparatus in which discharge cells are formed between a rear substrate with barrier ribs formed thereon and a front substrate facing the rear substrate, and when an inert gas inside each discharge cell is discharged by a high frequency voltage, vacuum ultraviolet rays are generated to illuminate phosphor to thereby allow displaying of images.
FIG. 1 is a plan view showing electrodes formed on a general PDP, and FIG. 2 is a sectional view showing a discharge cell of the general PDP.
To begin with, discharge cells are formed by a plurality of barrier ribs 24 separating a discharge space on a rear substrate 18 facing a front substrate 10.
An address electrode 12X is formed on the rear substrate 18, and a scan electrode 12Y and a sustain electrode 12Z are formed as a pair on the front substrate 10.
As shown in FIG. 1, the address electrode 12X crosses the other electrodes, and in this respect, the rear substrate 18 in FIG. 2 is shown as having been rotated by 90° for the sake of explanation.
A dielectric layer 22 for accumulating wall charges is formed on the rear substrate 18 with the address electrode 12X formed thereon.
The barrier ribs 24 are formed on the dielectric layer 22 to define a discharge space therebetween and prevent a leakage of ultraviolet rays and visible light generated by a discharge to an adjacent discharge cell. Phosphor 20 is coated on the surface of the dielectric layer 22 and on the surface of the barrier ribs 24.
Because an inert gas is injected into the discharge space, the phosphor 20 is excited by the ultraviolet rays generated during a gas discharge to generate one of red, green and blue visible light.
The scan electrode 12Y and the sustain electrode 12Z formed on the front substrate 10 include transparent electrodes 12a and bus electrodes 12b, respectively, and cross the address electrode 12X.
A dielectric layer 14 and a protective film 16 are formed to cover the scan electrode 12Y and the sustain electrode 12Z.
The discharge cell with such a structure is selected by a facing discharge formed between the address electrode 12X and the scan electrode 12Y, and the discharge is sustained by a surface discharge between the scan electrode 12Y and the sustain electrode 12Z, to thus emit visible light.
FIG. 3 is a front view of the general PDP.
The PDP includes an exhaust tip (T) formed at an outermost portion thereof to exhaust impurities present inside the panel during an exhausting process. In this respect, however, in the exhausting process, impurities may not be completely exhausted out of the panel but remain around the exhaust tip (T) to contaminate a cell.
To avoid such a problem, contamination preventing cells (D) are formed at a non-valid screen (B) outside a valid screen (A) on which an image is displayed, to induce contamination generated by the impurities that have not been exhausted thereto.
However, because a bus electrode and a transparent electrode are not formed on the non-valid screen (B) with the contamination preventing cells (D) formed thereon, impurities present inside the contamination preventing cells (D) affect discharge cells of the valid screen (A), which may cause an erroneous discharge that generates unwanted spots and flashes.
In particular, metal impurities such as Pb, Ca and Na are adhered onto the dielectric layer made of MgO, which reduce the surface resistance of the dielectric layer and cancel out wall charges during the discharge, which causes illumination failures, and as a result, the driving voltage to make sure that discharges occur properly must be increased.